The effects of lead in the development of the central nervous system are studied by means of microscopies (light and electron microscopy) and autoradiography. It is found that lead is moderately teratogenic in both chicks and mice. Malformed nervous system was observed. Histologically, the lesions were vascular-type including hemorrhage and edematous changes. Some thinning of myelination is also evident. EM-histochemistry also revealed the intracellular localization of lead in the cyoplasmic membranes and organelles. Preliminary study suggested a reduction of protein synthesis associated with the intoxicated brains.